public class SingleLinkedList {
    static class ListNode {
        public int val;
        public ListNode next;

        public ListNode(int val) {
            this.val = val;

        }
        public ListNode(){

        };
    }

    public ListNode head;
    public boolean hasCycle(ListNode head){
        if(head==null){
            return false;
        }
        ListNode fast=head;
        ListNode slow=head;
        while (fast!=null&&fast.next!=null){
            fast=fast.next.next;
            slow=slow.next;
            if(fast==slow){
                return true;
            }
        }
        return false;
    }
}
